Plasma doping system for 200 and 300 mm wafers

A plasma doping system has been built for 200 and 300 mm wafer implantation in the 80-10,000 volt range. The architecture and operational performance of the tool is described and results are shown for dose accuracy, wafer charge and contamination control. Two process chambers are used to isolate p- and n-type dopants and can be dedicated to a variety of dopant gases. Each process chamber features plasma processing with pulse-initiated plasma formation. This method minimizes etching and contamination effects by reducing the total exposure of the system to plasma for a given implant in comparison to conventional PIII processing. A novel method of plasma ignition is used to allow plasma doping below the normal Paschen limit for cathodic pulse plasma ignition and is capable of producing practical implants below 100 volts. The wafer handling system is based on the VIISta-series implanter end station used in the new 300 mm line of implant tools produced by Varian. Two vacuum load locks feed a two chamber cluster tool architecture. Each process chamber is equipped with a mass flow controller and valve-orifice controlled pressure regulation system and process control is achieved by setting the anode-cathode spacing, the process pressure, energy and dose. Dose control is obtained by use of pulse by pulse charge integration of currents representative of the wafer sheath current. First order correction of the displacement current is done prior to the integration process.